1. Field of the Invention
This invention relates to papermakers' double layer type fabrics.
2. Description of the Prior Art
There have heretofore been many requirements for papermakers' fabrics. The requirements may be roughly sorted into the following three groups:
Group I Prevention of generation of wire marking, sufficient tanglement of cellulosic fibers, and problems as to the quality of paper or as to the retention of paper obtained; PA1 Group II Improvement in wear resistance of fabrics and extension of the service life thereof; and PA1 Group III Satisfactory drainage, and the like.
The requirements in the respective groups are associated with one another in many respects. Roughly speaking, the problems in group I are greatly associated mainly with the structure of the papermaking side surface of the fabric, the problems in group II are greatly associated with the structure of the running side surface (which is the reverse side surface or roller side surface) of the fabric, and the problems in group III are associated with the entire fabric.
There have heretofore been proposed many approaches to the solution of the problems in group I. However, there have not been made sufficient efforts to improve the papermakers' fabrics in wear resistance except that the running side of the fabric has been made to take a wefts-wearing form only to prevent the warps of the fabric from being worn.
On the other hand, there have recently been made many requirements such as the rate of papermaking, an increase in amounts of filler used, an increased necessity of manufacturing neutral paper, and, in addition, a serious problem has been raised as to the wear resistance of the papermaking fabrics.
To improve the papermakers' fabrics in wear resistance, it has been attempted to use polyamide yarns but papermakers' fabrics in which polyamide yarns are used are defective in that they are apt to stretch and have poor runability (posture or shape stability).
Thus, polyester yarns which are poor in wear resistance but excellent in rigidity, have heretofore been mainly used in the preparation of papermakers' fabrics which are stretchable with difficulty and excellent in runability.
In such heretofore-used papermakers' fabrics, the crimps of wefts in the running side surface (which is the reverse side surface or roller side surface of the fabric) are identical in length with one another and are short as explained with reference to FIG. 59 which will be stated later. It has been attempted to improve even such conventional papermakers' fabrics use of yarns having a large diameter as wefts in the running side surface of the fabric, whereby the fabrics are improved in wear resistance to some extent but the thus improved fabrics are defective in that, because the wefts are large in diameter, the balance between the wefts and the warps is lost so that the crimpness is affected and wire marking occurs. Thus, such conventional improved papermakers' fabrics are those which raise too many problems from the standpoint of their practical use.
In addition, as is understood from the problems of Group III, a change in the structure of the running side surface will affect the drainage of the fabric and the problems will not be solved by a makeshift means such as the use of large wefts in the running side surface.